Oil stripping fryer unit

ABSTRACT

A continuous oil fryer used to fry food slices, such as potato chips, having an internal oil stripping capability. The fryer accumulates the steam produced by the frying process in a hood and utilizes such steam, after superheating the steam by passing it through a heat exchanger, to strip oil from product immediately upon removal from the hot oil bath by passing the superheated steam through a product bed while on an output conveyor. The superheated steam removes oil from the product on the output conveyor without increasing the moisture level of the product. The fryer therefore accomplishes the same function as a low-oil stripper without increasing the footprint of the frying unit and with less energy.

PRIORITY CLAIM

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a fryer assembly having an oilstripping capability integral to the unit. More particularly, theinvention relates to the extension of the steam collection hood on achip frying unit and the incorporation of oil stripping features in suchextended hood, thereby eliminating the need for a separate low-fatstripping unit.

2. Description of Related Art

Food pieces, such as potato chips, are commonly cooked in hot oil in afryer, such as a Heat and Control PC-50 fryer. A simplified schematicillustration of such a continuous fryer is shown in FIG. 1.

Referring to FIG. 1, the food pieces, such as potato slices, areinserted into the fryer unit by means of a infeed conveyor 102. Theslices then float in the hot oil 104 until removed from the fryer unitby an output conveyor 106. Agitation paddles (not shown) and a submerger105 can be used to keep the slices from clumping together and floatingto the surface of the oil 104. The fried food pieces on the outputconveyor 106 are in a bed arrangement, as opposed to single chips in amonolayer arrangement, and are therefore referred to as a product bed120 on the conveyor 106.

The food pieces are dehydrated during the frying process and, therefore,release moisture in the form of steam. This steam is collected by a hood108 located above the oil 104. As shown in FIG. 1, it is common toexhaust the steam collected by such hood by one or more large exhaustfans 110 associated with one or more exhaust ports 112, as illustratedby the arrows within the hood 108. The steam temperature within suchhood is typically in the range of 220° F. to 260° F., or normally about240° F. The collected steam from the exhaust ports 112 is typicallycondensed, collected, and discarded or used in other unrelatedprocesses. Thus, in most prior art applications the latent heat of thesteam is essentially lost in the process.

Absent further processing to reduce the amount of oil in the chipsproduced by the fryer illustrated in FIG. 1, typically potato chips exitsuch fryer ready for seasoning and packaging with a total oil content byweight of approximately 36% and preferably a moisture level of about1.1-1.5% by weight. In order to reduce the oil level of such chips,however, the chips can be routed directly from the frying unitillustrated in FIG. 1 by means of the output conveyor 106 to a low-fatstripping unit as illustrated in FIG. 2. This output conveyor 106remains enclosed such that the fryer of FIG. 1 and the low-fat stripperof FIG. 2 are in communication with each other and each is a part of asingle enclosed system.

FIG. 2 is a simplified schematic illustration of a prior art low-fatstripping system or unit, also referred to as a low-fat stripper, suchas the model LFSS manufactured by Heat & Controls of Hayward, Calif.Product, such as potato chips, enters the low-fat stripper by means ofan infeed conveyor 206, which has received the product from the outputconveyor 106 of FIG. 1 or is simply a continuation of said outputconveyor 106. The conveyor belt on such infeed conveyor 206 is porous,thereby allowing fluids, such as oil dripping off the product bed 220,to easily pass through the belt. Superheated steam is forced at highvelocity through the product bed 220 while the product is on the infeedconveyor 206. This steam strips oil from the surface of the chips. Thestripped oil drops to the base of the low-fat stripper or is carriedwith the steam as it exits the product bed 220.

The steam then flows through an oil separator 222 before being blownthrough a heat exchanger 224 to be reused again for stripping of theproduct bed 220. The heat exchanger 224 adds heat to the steam to keepit in a super-heated state. Steam is also constantly generated and addedto the low-fat stripper to replace steam vented back to the fryer andlost elsewhere in the system. The steam is circulated throughout theentire unit (as illustrated by the arrows) by a high-volume fan 226. Thestripped product exits the unit via an output conveyor 228.

The low-fat stripper recycles some of the steam it uses and removes someof the oil from the product. Potato chips made using a low-fat strippertypically have a finished oil content by weight of between 20% and 28%and a finished moisture level of about less than 2%.

The steam in the low-fat stripper is superheated to typically in therange of 290° F. to 320° F. The pressure in the low-fat stripper unit ismaintained at approximately ambient conditions. The velocity of thesteam as it blows onto the product bed is in the range of 1,500 ft./min.to 2,500 ft./min. The use of superheated steam in the stripper isimportant, because if steam at lower temperatures is used the producttends to absorb moisture from the steam. Adding moisture back into theproduct at this stage is generally undesirable, as it is preferred thatthe product exit the stripper at or below 2% moisture by weight for,among other reasons, longer shelf stability.

The low-fat stripper, as noted previously, is a separate unit from thefryer illustrated in FIG. 1. As a consequence, a product line thatincorporates a low-fat stripper requires a larger plant footprint. Inaddition, the low-fat stripper is a capital expenditure above and beyondthe cost of the fryer itself. There are energy costs as well when steamproduced by the fryer is discarded while steam is constantly added andheated in the stripper.

Low-fat strippers such as the one described above require the use oflarge amounts of steam at very high velocities to effectively strip theproduct of a meaningful amount of oil. It is now understood that thereason for this high-energy requirement relates to the amount of timethat it takes to get the product from the cooking oil 104 of FIG. 1 intothe low-oil stripper of FIG. 2. During the transit time from the oil tothe stripper, the product cools and continues to absorb oil. One of themechanisms for reducing the oil in the chip is to heat the chip outsideof the oil environment so that the dehydration of the chip drives theexpulsion of oil from within the chip and off of its surface. In otherwords, the continued release of water vapor or steam from within thechip provides a mechanism for removing oil from the chip. When the chipis allowed to cool prior to exposure to superheated steam, much moreenergy or work is required to remove any substantial amount of oil fromthe chip. Unfortunately, since the oil stripper and the fryer are twoseparate units, the transit times between removal from the oil untilentrance into the stripper can be in the range of 40 seconds to a minuteor more. During that time, the chips cool considerably, making it thatmuch more difficult to remove the oil from the chips.

Consequently, a need exists for combining the low-fat strippercapabilities of reducing the oil content of the finished fried chipswith the basic equipment of existing fryers. This new apparatus shouldminimally affect the equipment footprint of a stand-alone fryer whileutilizing the steam produced in situ. Such unit should amount to adecrease in energy usage, decrease in plant footprint, decrease incapital outlay per line, and yet provide finished product chips with areduced fat content and low moisture content similar to chips producedwhen an oil stripper unit is used.

SUMMARY OF THE INVENTION

The present invention involves a modification to existing hooded fryerdesign in order to combine the functionality of a low-oil stripper withthe fryer unit. In one embodiment of the present invention, the steamvents in the fryer hood over the hot oil are blocked off or restrictedso that the steam accumulates in the hood as opposed to immediatelyventing. The steam is then drawn towards what is normally the exit endof the fryer by one or more fans positioned inside the hood or in anexhaust port at the exit end of the fryer. The steam is then passedthrough a heat exchanger, thereby pre-heating the steam to a superheatedstate, typically in the range of 300° F. to 310° F. This superheatedsteam is then passed through the product bed as the product is exitingthe fryer on the output conveyor. Thus, the steam generated by fryingthe product is used to strip the product of excess oil all in the sameunit.

The present invention is an improvement over the prior art in thatcombining the functionality of a low-oil stripper within a fryer hoodreduces the overall equipment footprint and takes advantage of the steamproduced in the fryer for use as the stripping steam. Applicants'invention decreases the overall energy use on a low-fat product line,decreases the plant footprint for such product line, and decreases thecapital outlay required to set up such product line. Yet, Applicants'invention produces low-fat chips with the requisite low moisture levels.

These as well as additional features and advantages of the presentinvention will become apparent in the following written description.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asa preferred mode of use, further objectives and advantages thereof, willbe best understood by reference to the following detailed description ofillustrative embodiments when read in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a schematic illustration of a prior art fryer;

FIG. 2 is a schematic illustration of a prior art low-fat strippingunit; and

FIG. 3 is a schematic illustration of a fryer with built-in strippingcapabilities of one embodiment of Applicants' invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 is a simplified schematic representation of one embodiment ofApplicants' invention. As with a prior art fryer, Applicants' continuousfryer comprises a steam hood 308 which collects the steam produced insitu by product being fried in the hot oil 304. The product is likewiseintroduced into the fryer by an infeed conveyor 302. However, the hood308 of Applicants' invention does not necessarily exhaust the producedsteam through exhaust ports 340 located above the frying product, as isillustrated by the exhaust ports 112 in FIG. 1. In fact, a prior artfrying unit can be modified by simply closing off or restricting anysuch exhaust ports 112 or can maintain one or more such ports 340 (FIG.3) with an adjustable door or closing means 338 that can restrict theflow of steam through the port 340.

As illustrated in FIG. 3, Applicants' fryer comprises one or more flowinducing devices 310, 311, such as a fan 310, for the purpose of flowingthe steam through the hood from an upstream position near the sliceinfeed 302 to a downstream position near the output conveyor 306. Suchone or more fans 310, 311 can be located in any number of areas in thehood, such as before or after the heat exchanger 324, provided that thefans induce the flow as will be described herein. For example, andwithout limitation, a single exhaust fan 311 can be located in theexhaust port 312 at the downstream end of the unit. This exhaust fan 311can operate alone or in conjunction with one or more other fans 310located within the hood 308. Likewise, one or more fans 310 located inthe hood 308 can drive the steam flow with or without the benefit of anexhaust fan 311. The location, number and type of fans 310, 311 usedwith Applicants' invention is dependent on the desired flowcharacteristics, velocities, and product applications.

Applicants' invention further consists of a heat exchanger 324 locatedwithin the hood. This heat exchanger is located in close proximity tothe output conveyor 306. The heat exchanger 324 is upstream from a flowdiversion component 330 that is used to direct steam after it has passedthrough the heat exchanger 324 towards the product bed located on theoutput conveyor 306. The area on the output conveyor 306 that is exposedto the steam flowing through the product bed is referred to byApplicants as an oil stripping zone 332. This oil stripping zone 332 isnecessarily located between the heat exchanger 324 and the flowdiversion device 330. The output conveyor 306 is constructed of a porousmaterial or design that allows for the free flow of the steam throughthe product bed found on the output conveyor 306 and through the outputconveyor 306 itself. Once the steam is blown through the product bed onthe output conveyor 306 the steam is directed out of the fryer by way ofthe exhaust port 312 which is accessed from an opening 344 downstream ofthe oil stripping zone. Product is removed from the output conveyor byway of a rotary air lock 336. Because of the rotary air lock 336, steamcannot exit the hood 308 after flowing through the stripping zone 324 byany means other than the exhaust port 312 by way of an opening 344 intosaid port 312.

The steam flow through the hood 308 from upstream to downstream isillustrated by the flow arrows shown in the hood 308. In a preferredembodiment, steam is collected in the hood 308 in the temperature rangeof about 212° F. to about 300° F. The steam is then passed through theheat exchanger 324 in order to raise the temperature of the steam topreferably in the range of about 280° F. to about 320° F. or morepreferably in the range of about 300° F. to about 310° F. Steam pressurewithin the unit is maintained at approximately ambient levels. The steamis next directed through the product bed and the output conveyor 306 atthe oil stripping zone 332. The velocity of this steam as it is blownthrough the oil stripping zone 332 (passes through the food pieces) is,in a preferred embodiment, less than 1,000 ft./min., and more preferablyabout 250 ft./min. to about 500 ft./min. This flow rate corresponds to aproduct production rate of about 2,000 lbs./hr. to 40,000 lbs./hr. and asteam production rate within the hood of about 500 lbs./hr. to about10,000 lbs./hr.

Applicants have found that much lower velocities can be used for thestripping steam than has been used in the past in low-oil strippers.This is believed to be a result of not allowing the product to coolprior to stripping. The product bed is subjected to super heated steamas soon as possible after removal from the oil 304. Because the steam issuper-heated as it passes through the oil stripping zone 332, the foodpieces on the output conveyor 306 continue to cook, thereby drivingmoisture out of the food piece. This continuous cooking, without a cooldown while the product is in transit to the stripper as occurs in theprior art, inhibits the absorption of further moisture by the foodpieces from the contact with the steam and more efficiently drives oilout of the chip, which is then more easily stripped by the steam.Importantly, the prior art methods involve an elapsed time of typically30 to 60 seconds, between the time product is removed from the oil 304and when it is subject to steam stripping. Applicants' invention reducesthis elapsed time to 10 seconds or less, because the product is strippedimmediately after leaving the oil 304. In fact, it is preferred thatstripping occur within 5 seconds of removal of the product or foodpieces from the hot oil 304 by the output conveyor 306. In order toaccomplish this timely stripping, the oil stripping zone 332 must startwithin a close proximity to the oil 304, preferably within three feetthereof, and more preferably within two feet thereof. Thus, the oilstripping zone 332 starts within three feet of the point where theoutput conveyor 306 is in communication with the oil 304.

After passing through the oil stripping zone 332, the steam can befurther blown through an oil separator 322 before being exhausted fromthe frying unit. The recovered oil from the steam is then returned tothe frying oil via an oil collection point 334 for further use.Alternatively, since virgin steam is being constantly produced in thehood 308, the steam can be exhausted without passing through an oilseparator 332.

The steam temperature and flow rates can be adjusted as well as theproduct throughput in order to obtain the desired reduction in oilcontent of a food piece fried with Applicants' fryer. The volume of thesteam can also be adjusted by a door 338 on an exhaust or relief port340 (with its exhaust fan 342) located upstream of the heat exchanger.When excess steam collects in the hood 308, the door 338 is opened onthe relief port 340 in order to vent the excess steam prior to the steampassing through the heat exchanger 324. If necessary, a fan 342 can beactivated to draw the excess steam out of the hood 308. The size of theopening obtained by opening the door 338 and/or the fan 342 speed can beadjusted to ensure the desired amount of steam is removed.

In a preferred embodiment, Applicants' modified fryer produces potatochips having a finished oil content of about 28% to about 31% by weight.These potato chips also have a low moisture level, typically about 1.1%to about 1.5% by weight due to the use of the super-heated steam aspreviously described. Yet, Applicants' invention uses less energy toaccomplish this stripping.

One embodiment of Applicants' modified fryer is constructed by modifyingexisting hooded continuous fryers by sealing off the exhaust portslocated above the frying oil, adding an internal heat exchanger and flowinducing device, and constructing the downstream portion of the fryersuch that it directs the steam through the oil stripping zone and out anadded exhaust port that defines the furthest downstream point of steamwithin the fryer. In an alternative embodiment of Applicants' invention,a hooded continuous fryer is constructed of a hood having no orcloseable/adjustable exhaust ports above the frying oil and the sameconfiguration of the downstream heat exchanger, diversion device, andexhaust port as previously described.

The foregoing is merely illustrative of the principles of thisinvention, and various modifications can be made by those skilled in theart without departing from the scope and spirit of the invention. Forexample, while the invention has been described in the context of apotato chip frying line, it should be understood that the invention andprinciples involved therein are applicable to the cooking and strippingof any fried food piece, such as fried fruit chips, fried vegetablechips, other fried tuber slices such as sliced sweet potatoes, andfabricated food slices made from sheeted dough as well such asfabricated potato chips, tortilla chips, and corn chips, and otherfabricated vegetable and/or fruit based chips. Thus, the startingmaterial can be either a raw food piece or a fabricated food piece madefrom sheeting a dough, any of which results in an end productgenerically referred to by Applicants as a “chip.” Applicants' inventionis applicable to all hooded continuous fryers used to cook food piecesof any type.

1. A continuous food fryer, said fryer having a steam hood defined by anupstream end near the product input into the fryer and a downstream endnear the product output from the fryer, said fryer comprising, a steamflow inducing device which promotes the flow of steam from upstream todownstream through the steam hood; a steam exhaust port defining thefurthest downstream point of steam within the fryer; an output conveyorlocated under the hood at the downstream end of the fryer, wherein saidoutput conveyor is in communication with hot oil; an oil stripping zoneon the output conveyor, said zone located upstream of the exhaust port;and a heat exchanger within the hood and located upstream of the oilstripping zone.
 2. The fryer of claim 1 wherein said steam flow inducingdevice comprises at least one fan located within the hood.
 3. The fryerof claim 1 wherein said steam flow inducing device comprises an exhaustfan associated with the steam exhaust port.
 4. The fryer of claim 1further comprising an oil separator located in the steam exhaust port.5. The fryer of claim 1 wherein the oil stripping zone starts withinthree feet of the point where the output conveyor is in communicationwith the hot oil.
 6. A method for reducing the oil content of fried foodpieces using a hooded continuous fryer, wherein said fryer comprises aheat exchanger located within the hood and an output conveyor whichremoves food pieces from hot oil, said method comprising the steps of:a) collecting in the hood steam generated by frying of the food pieces;b) passing said collected steam through a heat exchanger, therebyheating said steam to at least 280° F.; and c) passing said heated steamof step b) through the food pieces while on the output conveyor, therebystripping oil from said food pieces.
 7. The method of claim 6 whereinthe velocity of the heated steam at step c) through the food pieces isless than 1,000 ft./min.
 8. The method of claim 6 wherein the velocityof the heated steam at step c) through the food pieces is about 250ft./min. to about 500 ft./min.
 9. The method of claim 6 wherein thesteam is heated at step b) to between about 300° F. and about 310° F.10. The method of claim 6 further comprising the step of: d) exhaustingthe steam from the hood after step c).
 11. The method of claim 6 furthercomprising the step of: d) flowing the steam through an oil separatorafter step c).
 12. The method of claim 6 wherein step c) occurs within10 seconds of the removal of the food pieces from the hot oil.
 13. Themethod of claim 12 wherein step c) occurs within 5 seconds of theremoval of the food pieces from the hot oil.
 14. The method of claim 6wherein step a) further comprises venting outside the hood some of thesteam generated by the frying of the food pieces prior to step b). 15.The method of claim 6 wherein said fried food pieces are chips selectedfrom the group consisting of potato chips, tortilla chips, corn chips,fruit chips, and vegetable chips.
 16. The chips produced by the methodof claim
 15. 17. An improved method for stripping oil from a productcooked in a hot oil fryer wherein said improvement comprises strippingoil while the product is still within a hot oil fryer and with 10seconds of the product's removal from the hot oil.
 18. The improvedmethod of claim 17 wherein the improvement further comprises using steamproduced in situ in said hot oil fryer to strip the oil from theproduct.
 19. The improved method of claim 17 wherein said food productis chips selected from the group consisting of potato chips, tortillachips, corn chips, fruit chips, and vegetable chips.
 20. The chipsproduced by the improved method of claim 19.